Hydroforming with recycling of part of the products



Nov. 3, 1959 M. w. LEIGH ETAL 2,911,358

HYDROFORMING WITH RECYCLING OF PART OF THE PRODUCTS Filed June 30, 1955HOT BLOWER HEAT EXCHANGER HALOGEN PRODUCT Marjorie W Leigh Alberf B.Wehy, Jr

Ri h d w Sag? Inventors Randolph M. Ball/y By f'forney United StatesPatent Ofiice 2,911,358 Patented Nov. 3, 1959 HYDROFORMING WITHRECYCLING OF PART OF THE PRODUCTS Marjorie W. Leigh, Short Hills, AlbertB. Welty, Jr., Westfield, Richard W. Sage, Fanwood, and Randolph M.Bailly, Little Silver, N.J., assignors to Esso Research and EngineeringCompany, a corporation of Delaware Application June 30, 1955, Serial No.519,146

3 Claims. ,(Cl. 208-139) The present invention relates to improvementsin the hydroforming operation. More particularly, the present inventionrelates to improvements in supplying heat to the hydroforming process bymeans which are more economical, more effective, give an improvedproduct and otherwise are more efiicient.

The application of Charles E. Hemminger, Serial No. 367,631, filed July13, 1953, describes and claims a method of recycling a portion of thehydroformed product to the reaction zone.

Hydroforming may be indicated or defined as a process for the catalyticconversion of feed stocks boiling in the naphtha boiling rangeto formproducts of improved octane rating by contacting the naphtha feed with asolid catalytic material in the presence of hydrogen at elevatedtemperature and pressure. As feed stock, virgin naphtha, crackednaphtha, Fischer naphtha, or a mixture of these may be employed. Thecatalysts employed are usually supported members of the platinum groupmetals or the V or VI group metal oxides also supported on a carrier.Specifically, the most commonly'used catalysts are platinum carried onalumina and molybdenum oxide carried on alumina.

The present invention relates to hydroforming in the presence ofplatinum group metal catalysts.

As commonly described in the literature and practiced commercially,recycled hydrogen, that is, a hydrogencontaining gas obtained from aproduct recovery system is heated separately or in admixture with thefeed and introduced into the reaction zone with the feed oil. In priorpractice, this recycled gas was used to add the heat required for theendothermic reaction by heating the recycled gas from about 100-150 F.to a temperature within the range of from about 10001200 F. andrecycling it in amounts of from about 2,00010,000 standard'cubic feet of.gas per barrel of oil feed to the reaction zone. Aside from the factthat this recycled gas is associated with hydrocarbons which undergothermal cracking during the heating of the gas to form carbonaceousdeposits in the heating apparatus and the transfer lines, there is thefurther disadvantage that large furnace capacity is required because ofthe large quantities of gas thus recycled and the large amount of heatrequired to raise it to the stated temperatures. One of the importantaspects of the present invention is'-to'so operate the hydroformingprocess as to eliminate the necessity for recycling and reheating largequantities of relatively cold hydrogen-containing gas. g

As practiced commercially, hydroforming employing a platinum catalyst isusually carried out in a plurality of separate reactors through whichthe oil passes in series and in which the oil is reheated betweenstagesor reactors.

In brief compass, the present invention proposes carrying out ahydroforming process in the presence of a platinum group. metal catalystemploying a single reactor and supplying heat to the reaction zone byrecycling to the reaction zone a portion of the total reactor effluentinlet temperature, a difference of only about F the recycled materialhaving-the same composition as the reactor effluent. This procedure,therefore, permits the use of only one reactor since suflicient heat forreaction can be supplied with the recycled product to eliminate thenecessity for intermediate reheat stages. This scheme also eliminatesthe necessity for separately heating and recycling hydrogen-containinggas, thus reducing the heat exchange area and compressor power required.

In order to accomplish these results, it is necessary to observe certainoperating conditions and these include:

(1) Employing the regenerative hydroforming process wherein the catalystis regenerated periodically, preferably, with an oxygen-containing gas;

(2) Employing as feed a naphtha which contains not more than 0.01%sulfur, desulfurizing the feed, if necessary, before hydroforming byknown methods such as by treating the feed in the presence of hydrogenat elevated temperatures in the presence of a suitable catalyst, such ascobalt molybdate carried on alumina.

(3) Limiting the on-stream periods of the operation betweenregenerations of the catalyst to relatively short periods of time;

(4) Recycling a reheated portion of the hot effluent from the reactor;

(5) Operating with a high activity catalyst by providing means whereby ahalogen such as chlorine is maintained on the catalyst. v

These above specified conditions of operation, plus frequentregeneration of the catalyst, result in the provision of an integratedsystem which is adapted to pro vide important economies in thehydrofonning process.

The object of the invention is to provide an improved method ofhydroforming naphthas which results in effecting important economies inthe hydroforming process.

Other and further objects of the invention will be apparent from thefollowing more detailed description and claims;

In the accompanying drawing there is shown, diagrammatically anapparatus layout or system in which a preferred modification of theinvention may be carried into eifect.

Referring in detail to the drawing, a low sulfur naphtha feed isintroduced into the system through line 1 and thence pumped by pinup 2into line 3 by means of which it is passed to a heat exchanger 4 whereinit passes therethrough in heat exchange relationship with hot productacquiring heat from said product whereupon the preheated feed iswithdrawn from heat exchanger 4 through line 5 and charged to a heatingmeans 6 where it is further heated and thence withdrawn through line 7and charged to line 11 wherein it is mixed with a reheated portion ofthe effluent from furnace 18, such effluent being obtained from line 14through line 15, through hot blower 16, line 17 and reheat furnace'lSand line 8. Fresh feed and recycled material thence pass via line 11,carrying valve V into line 12 and thence into reactor 10. Reactor 10contains two separate bodies of catalyst, namely, C and C which arespaced apart as shown. The oil feed is injected into reactor 10 in thespace between the beds C and C The advantage of so charging the feed inthis manner is in the lower pressure drop across the reaction systemreducing the hot blower horsepower requirements.

Under conditions more fully set forth hereinafter, the desiredhydroforming reaction occurs and the reformed product is withdrawn fromreactor 10 via lines 13 and 14. The hot stream flowing in lines 13 and14 is in part passed without cooling via line 15 through a hot blower16, a line 17 and a reheat furnace 18 into line 8 for recycling aspreviously indicated. The material in line a 3 8 contains hydrogen as aresult of the dehydrogenation reaction occurring in reactor 10, and thisamount of hydrogen is sufficient to protect the catalyst against thedeposition of inordinately large amounts of carbonaceous and-otherdeactivating deposits on the catalyst. As previously stated, the heatcontent of this hot recycled product adds a very substantial portion ofthe heat necessary to support the endothermic reaction of hydroformingwhich occurs in reactor .10. The material in lines 13 and 14 whichpasses to product recovery passes through heat exchanger 4, thencepasses via line 20 into a cooler 21 wherein it is cooled to atemperature sufiiciently low to condense the normally'liquid material,say, to a temperature of about 100 F., whereupon the cooled material iswithdrawn from 21, through line 22, thence charged to a separator 23from which the hydr'oformed crude liquid product maybe withdrawn throughline 24 and passed to conventional distillation and other purifyingequipment to recover the desired product. Tail gas is withdrawn fromseparator 23, through line 25, and since this gas is rich in hydrogen,it will find use in the refinery in hydrodesulfurizing oil, insaturating olefins and other conventional refining processes.

There comes a time when the catalyst becomes contaminated withcarbonaceous deposits under severe conditions of operation employed inthe present improved process. Consequently, it is necessary to interruptthe on-stream hydroforming phase and to regenerate the catalyst. In sodoing, the oil feed to the reactor 10 is discontinued and valve V closedand the reactor de pressured through line 29 and flushed with a CO andCO free inert gas to drive oif volatile carbonaceous material. The inertgas enters the system through line 26, is sufficiently compressed in 27to give the desired flow rate through the system at a reasonable gasvolume, about 100 p.s.i.g., and thence passes via line 36 to furnace 37,withdrawn via line 28 carrying control valve V and charged to reactor10. The flow of hot inert gas is continued until the gas withdrawnthrough line 29 is substantially free of hydrocarbons. At this pointcompressor 30 iscommissioned for flue gas recycle through lines 32 and33, drier 34, lines 35 and 36 and furnace 37 to reactor 10. Air isintroduced through line 26 to compressor 27 and is mixed with therecycled inert gas in line 36 and passes to furnace 37, line 28 carryingvalve V through line 12 and into reactor 10, the concentration of oxygenin the mixture of air and recycled inert gas being about 2%. It is notedthat normal refinery inert gas is not employed to purge the catalyst,for experience has shown that carbon dioxide is reduced in the presenceof hydrogen and the platinum catalyst giving carbon monoxide, whichpoisons the platinum catalyst. Once the hydrogen is purged, the CObearing gases have relatively little poisoning action. The presence ofoxygen in the regeneration gas causes carbonaceous and other deposits tobe burned to form fumes which pass through lines 13 and 14 into valvedline 31 and are purged from the system through valved line 29. A portionof the flue gas is recycled to maintain the low oxygen concentrationdesired. The flue gas recycled is dried to remove water which wouldstrip the halogen from the catalyst. The burning of the carbonaceousdeposits on the catalyst, of course, increases the temperature of thecatalyst beds C and C but the oxygen concentration and gas inlettemperatures are carefully controlled so that the temperatures do notexceed l 0-1100 F. After the carbon is substantially completely burned0E as indicated by the temperature profile of the catalyst bed, theregeneration .gas entering through line 28 is increased to substantiallypure air, the flue gas recycle flow having been gradually de creased to0 after the-carbon has been burned off as pre viously mentioned. Theflow of heated air is continued thereafter for a period of about '4hours or until the catalyst is substantially restored in activity.Following the regeneration. period, the catalyst ispur'ged with an inertCO and CO free gas to remove oxygen from the catalyst beds, whereupon arenewal of the on-stream period is begun by first feedinghydrogen-containing gas to reactor 10 until the inert gas, such as N orscrubbed flue gas, has been substantially removed, and thereafter theoil feed is delivered to the reactor 10 and the on-stream period ofhydroforming is renewed.

If, after a number of cycles, including the on-stream phase, theregeneration and the purges described above, the catalyst is notsufliciently restored to a high level of activity, this insuificiencymay be corrected by treating the carbon-free catalyst with either pureoxygen or air at 100-400 pounds pressure at 1100ll50 F. This treatmentcorrects abnormalities in the platinum crystal size or form so as torestore the activity of the catalyst by reducing the crystal size andcausing the platinum particles to have a substantially amorphous formand an average crystal size of approximately 50 A. or less.

In order that the catalyst have a high level of activity, it isnecessary to include a halogen in the catalyst composition. Since thehalogen tends to be lost by the catalyst, it may be necessary toreplenish the halogen by addition of carbon tetrachloride, HCl or anyvolatile organic chloride to the feed flowing in line 3, Fig. 1 asindicated, the amount of said chlorine being such as to maintain fromabout 0.1 to 2.0 wt. percent chlorine based on the total weight of thecatalyst. Conventional means for halogen addition can be employed.

If product octane is a primary consideration, increasing the averagehalogen concentration on the catalyst either by higher addition ratesduring reaction cycles or by treating the catalyst after regenerationmay be employed. The higher activity obtained in this manner reducescatalyst selectivity to liquid product, however, and requires corrosionprotection for the unit.

To recapitulate, the present invention relates to a hydroformingoperation carried out with a platinum group metal catalyst and involvesas one of its chief features, the recycling to the reaction zone of'areheated portion of the total product, that is to say, recycling hotproduct of the same composition as the effiuent from the hydro formingreactor which is delivered to product recovery. The process is furthercharacterized in that it is of the regenerative type conducted atrelatively low pressures and without the use of recycled gas from theproduct recovery system and limiting the on-stream period to from about25-50 hours. Treatment of the catalyst with a halogen to maintain itsactivity, particularly, with respect to its hydrocracking activity andthe production of a hydroforrnate of good volatility characteristics isalso an important feature of the present invention.

The present process is adapted to produce a product having an octanerating as high as 95 research octane number. (clear) in yields of theorder of 82-83 volume percent C hydrocarbons based on feed.

The invention herein described has, as stated, many important features,principal of which is the utilization of the high heat carrying capacityof the reactor effluent in several important ways.

. First: Because of the higher heat capacity of the reactor efiluent ascompared with conventional recycle gas, less has to be circulated tosupply the same effective heat.

Gas stream B.t.u./s.c.f./ "F. Conventional recycle gas (91% H 0.023Reactor effluent (50% H 0.104

Second: Because the recycled stream goes through no heat exchangeequipment and because only a small amount of heat must be added in thefurnace to bring the recycle stream to the desired temperature, thecircuit pressure drop is very low and the normally used and expensiverecycle gas compressor can be replaced with the cheaper and lowercapacity hot blower 16 shown in Fig. 1.

Third: The reactor efliuent is at most only 100 below the desiredtemperature for reentering the reactor. This eliminates the necessityfor reheating cold recycle gas obtained from the product recovery systemwhich in turn means a substantial reduction in furnace requirements,heat exchangers, transfer lines, valving and the other accessoryapparatus which are employed inconventional hydroforming plants. IAnother important feature of the present invention is that, in itspreferred modification, ,it involves a single hydroforming reactor Ofcourse, if it is desired to produce a hydroformate continuously, asecond reactor may be included so that while the'catalyst is undergoingregeneration in one reactor, the other reactor would be on-stream.

The present studies have revealed that practical operating conditionspermitting the use of only recycled product in a single on-streamreactor system lie within a very narrow range. Furthermore, low sulfurin the feed is required for practical operation. The desired productquality, deactivation of the catalyst, and the time required forreactivationare determining factors which control the conditions. Theconditions which were found to give good results are:

1) A virgin naphtha which normally boils at from about 200350 F. andcontains 30+ percent of naphthenes, the remainder paratfins andaromatics, and should contain less than 0.01 wgt. percent sulfur.

(2) Single adiabatic reactor.

Example There is set forth below a specific example illustrating thepreferred modification of the present invention:

Catalyst employed: Platinum on alumina. 0.6 wt. percent platinum withcrystals below 50 A. on 100% eta alumina made by the alcoholate method.Chlorine on catalyst after chlorine treatment, about 1-2 wt. percent oncatalyst.

Cycle length on oil feed hours 35 Unit pressure p si e 300 Feed ratew./hr./w. 2 Product recycle s.e.f./b. of feed 11,000 Hydrogen intoreactor mol. percent 46 Reactor inlet temperature, F.:

At start 950 At end 965 Reactor outlet temperature, F.:

Start 866 Finish 895 Total temperature drop, "F 84-70 Product obtained:

C gasoline: Yield vol. percent on F.F. 85.2 Av. octane CFR-R Cl 92.5Reid vapor pressure, lbs. 4.2 Distillation-D-i-L, vol. percent 158 F.4.5 257 F. 49.5 356 F. 98.0 Butanes, vol. percent on ER 5.0

It will be understood that the foregoing conditions of operation aremerely illustrative and do not impose any limits on the invention. Thus,good results are secured by operating under the following conditionswith feed stocks usually available to'a refiner:

1 Actual O.N. loss feed to 3 to 4 by gradually increasing preheattemperature during the cycle.

The most suitable naphtha would be one boiling in the range of fromabout 220-350 F., which contained at least 30% naphthenes, the remainderbeing paraifin aromatics and in some cases, olefins.

'In the above example, it will be understood, of course, that theseapply for best results to naphtha feed which contained 41% naphthenesand had a research "octane number of 5 8. If there is a lesser amount ofnaphthenes in the feed, the hot product recycle rate may be some.- whatlower since the lower the naphthene content of the oil, the lower theheat of reaction. The preheat supplied by the feed oil is a constant fora given reactor temperature drop during the passage of oil through thereactor. Consequently, the above table of conditions relate to thecritical operating conditions for a specific naphtha feed oil, and theexperienced operator will be guided by these illustrative conditionswhen processing a naphtha feed of higher or lower naphthene content than41 volume percent in the feed and a research octane number higher orlower than 58.

Theabove table sets forth that the maximum preheat temperature should beabout 965 F. with fresh catalyst and a good operating temperature wouldbe around the range of 945 950" F., and as the catalyst tended todeactivate under the severe conditions set forth in the above table, thetemperature should be gradually increased so that at the end of, say, anon-stream period of about 50 hours, the octane number variation in theproduct can be held to 3-4 octane numbers. With respect to the pressure,of course, the lower the pressure, the higher the yields and the octanenumber of the product since catalyst activity and selectivity are bothadversely affected by high hydrogen partial pressures. However, in orderto protect the catalyst, pressures of about 200-300 p.s.i.g. arepreferred with the ordinary feed stocks.

From the foregoing description, it is to be noted that all of the heatnecessary to support the endothermic hydroforming reaction is obtainedby heat interchange of the cold feed with hot product, further heatingthe feed oil in, say, a furnace or pipe still to a temperature not exceeding about 1000" F. and supplying the remainder of the heat necessaryby recycling reheated hot total product to the reaction zone, the lattermeans supplying 70-90% of the total heat required. It is to be notedthat recycle gas is not recovered from the product recovery system at atemperature of about F. and heated to about 1200 F. as in theconventional process, thus achieving very substantial economies by theelimination of recycle gas reheating.

A mixed feed containing, say, virgin naphtha and cracked naphtha ornaphtha obtained from coking of heavy oil can be used as a feed. Thehydrogenation of the olefins present in the feed will, of course, addheat in situ and permit a reduction in the amount of heat added bypreheating the oil in a furnace, by reheating the recycled product,and/or will permit a reduction in the rate at which hot product need berecycled to the hydro forming zone.

What is claimed is:

1. Ina process of hydroforming a naphtha in a reac tion zonecontaining afixed bed of a catalyst which is a platinum group metal carried onalumina and containing a small amount of halogen, the improvement whichcomprises preheating a low sulfur naphtha stream to a temperature in therange of about 900 to 1000 F., passing the thus preheated naphtha streamto an inlet of said reaction zone from which hydrogen gas and naphthavapors pass through said fixed bed of catalyst to an outlet of saidreaction zone by which hydrogen gas and hydroformed naphtha product isremoved as a hot vaporiform efiluent, recycling a portion of said hotefiluent uncooled at a suflicient recycle rate andtemperature to saidinlet of the reaction zone for mixing with the preheated naphtha feedstream to make the resulting hydrogen gas and naphtha vapor mixture havea tempertaure in the range of 900 to 1000 F. on entering the fixed bedof catalyst from said inlet and to maintain a temperature drop from saidinlet to'the outlet of less than100 F., maintaining a pressure fromabout 200 to 500. psi. in said reaction zone, contacting said vapormixture with the catalyst for a period to etfect desiredconversion andrecovering a hydroformed product of high octane rating and ingoodiyields fromla portionrof the eflluent of said reaction zone;

2'. In the process of claim 1, said reaction zone containing twovertically spac'e'dbeds of the catalyst with the inlet at a pointbetween said spaced beds so that the'vapor mixture ofpreheatednaphthahydroforming feed mixed with the recycled hot efiluentcontaining hydrogen and hydroformed products is passed from said inletthrough each of said spaced beds to separate outlets.

3. The improvement in the process of claim 1 being further characterizedby the temperature of the vapor mixture at the inlet being at a maximumof=965 F. and the temperature of efiluent-in the outlet being in therange of- 866 to 895 P. so that the total temperature dropis in therange of about 70 to 84 F.

References Cited in the file of this patent UNITED STATES PATENTS2,334,553 Harding Nov. 16, 1943 2,479,110 Haensel Aug. 16, 19492,642,384 Cox June 16, 1953 2,692,847 Rex Oct. 26, 1954 2,749,285 FritzJune 5, 1956 2,773,013 Wolf et al. Dec. 4, 1956

1. IN A PROCESS OF HYDROFORMING A NAPHTHA IN A REACTION ZONE CONTAININGA FIXED BED OF A CATALYST WHICH IS A PLATINUM GROUP METAL CARRIED ONALUMINA AND CONTAINING A SMALL AMOUNT OF HALOGEN, THE IMPROVEMENT WHICHCOMPRISES PREHEATING A LOW SULFUR NAPHTHA STREAM TO A TEMPERATURE IN THERANGE OF ABOUT 900* TO 1000*F., PASSING THE THUS PREHEATED NAPHTAHASTREAM TO AN INLET OF SAID REACTION ZONE FROM WHICH HYDROGEN GAS NAPHTHAVAPORS PASS THROUGH SAID FIXED BED OF CATALYST TO AN OUTLET OF SAIDREACTION ZONE BY WHICH HYDROGEN GAS AND HYDROFORMED NAPHTHA PRODUCT ISREMOVED AS A HOT VAPORIFORM EFFULENT, RECYCLING A PORTION OF SAID HOTEFFULENT UNCOOLED AT A SUFFICIENT RECYCLE RATE AND TEMPERATURE TO SAIDINLET OF THE REACTION ZONE FOR MIXING WITH THE PREHEATED NAPHTHA FEEDSTREAM TO MAKE THE RESULTING HYDROGEN GAS AND NAPHTHA VAPOR MIXTURE HAVEA TEMPERATURE IN THE RANGE OF 900* TO 1000*F. ON ENTERING THE FIXED BEDOF CATALYST